I enjoy seeing Mounts run around my castle, but for the Crowns-Only Mounts, buying even one of them can be expensive, especially if you want one (or more) just to roam around your home.
Would the Professors ever consider allowing the 7-Day Mounts to roam the castle and not expire? This way, if one wanted multiple Dream Fillies and Swift Sharks to simply roam around their home, they would not have to pay full Crowns price for Mounts they do not plan on riding. It would be like buying a Crowns-Only housing item like the Krokotopian Sphinx.
If this were to become the case, I know I would definitely plan on buying up temporary Mounts with which to decorate my castle as soon as I can obtain the entertainment dollars to do so.